I've defined custom resolutions under a Windows XP installation, using a 31 Khz (minimum) CRT VGA monitor. So I can output 320x256 or 640x256 with 100 Hz (double PAL) refreshrate for example.
Are there any Archimedes/Risc PC emulators that support this in fullscreen? I tried a brief test with Sim City under RPCemu for example, but the lowest it goes for me is 640x480.